IF Statements

The %IF% construct gives TWiki the power to include content in topics based on the value of simple expressions.

%IF{"CONDITION" then="THEN" else="ELSE"}%

In the example above, if CONDITION evaluates to TRUE, then THEN will be included in the topic; otherwise ELSE will be included.

Note that because of the way TWiki evaluates, then whatever is in the THEN and ELSE parameters will already have been expanded by the time the condition is actually evaluated. The standard FormatTokens can be used in the THEN and ELSE parameters when you need to delay evaluation of (for example) a TWiki variable.

The basic syntax of a condition is the same as the syntax used for queries, with operators =, !=, ~, <, >, <=, >=, NOT, AND, OR, (), and functions lc(), uc(), d2n(). In addition, the following special operators are supported:

context

True if the current context is set (see below)

allows

'X' allows 'Y' is true if web/topic 'X' exists and allows access mode 'Y' for the current user. Web access rights are only checked if there is no topic called 'X'.

istopic

istopic 'X' is true if topic 'X' exists

isweb

isweb 'X' is true if web 'X' exists

ingroup

'X' ingroup 'Y' is true if user 'X' is in group 'Y'. 'X' can be a login name or a wikiname.

defined

True if a preference variable or url parameter of this name is defined.

$

expands a URL parameter or TWikiVariable name. Plugin handlers are not called. Built-in variables and user-defined preferences are supported. You can pass a limited subset of parameters to TWiki variables by enclosing the variable name in single quotes; for example, $ 'VARIABLE{value}'. The 'VARIABLE{value}' string may not contain quotes (' or ").

{X}

expands to the value of the configuration variable {X} - for example, {ScriptUrlPath}

Examples:

1. TWiki variable defined or not

%IF{"defined 'WIKINAME'" then="WIKINAME is defined" else="WIKINAME is not defined"}%

Configuration items are defined in configure. You cannot see the value of a configuration item, you can only see if the item is set or not.

Context identifiers are used in TWiki to label various stages of the rendering process. They are especially useful for skin authors to find out where they are in the rendering process. The following context identifiers are available:

set if {Register}{EnableNewUserRegistration} is on, and registrationis supported

passwords_modifyable

set if the password manager support changing the password / email

In addition there is a context identifier for each enabled plugin; for example, if GallousBreeksPlugin is installed and enabled, then the context ID GallousBreeksPluginEnabled will be set. Other extensions may set additional context identifiers.

The %IF% statement is deliberately kept simple. In particular, note that there is no way to conditionally execute a Set statement. If you need more sophisticated control over formatting, then consider using the SpreadSheetPlugin.

Note also that while the query syntax can be used to access form fields, there are some contexts in which an IF statement may be used where there is no topic context, or the topic context is not what you expected.